Data Sheet ADM1085/ADM1086/ADM1087
Rev. B | Page 11 of 16
APPLICATION INFORMATION
SEQUENCING CIRCUITS
The ADM1085/ADM1086/ADM1087 are compatible with
voltage regulators and dc-to-dc converters that have active high
or active low enable or shutdown inputs, with a choice of open-
drain or push-pull output stages. Figure 23 to Figure 25
illustrate how each of the ADM1085/ADM1086/ADM1087
simple sequencers can be used in multiple-supply systems,
depending on which regulators are used and which output
stage is preferred.
In Figure 23, three ADM1085s are used to sequence four
supplies on power-up. Separate capacitors on the CEXT pins
determine the time delays between enabling of the 3.3 V, 2.5 V,
1.8 V, and 1.2 V supplies. Because the dc-to-dc converters and
ADM1085s are connected in a cascade, and the output of any
converter is dependent on that of the previous one, an external
controller can disable all four supplies simultaneously by
disabling the first dc-to-dc converter in the chain.
For power-down sequencing, an external controller dictates
when the supplies are switched off by accessing the ENIN
inputs individually.
3.3V
DC/DC
IN
OUTEN
ADM1085
V
CC
ENOUT
3.3V
ENIN CEXT
V
IN
3.3V
2.5V
DC/DC
IN
OUTEN
ADM1085
V
CC
ENOUT
3.3V
ENIN CEXT
V
IN
3.3V
1.8V
DC/DC
IN
OUTEN
ADM1085
V
CC
ENOUT
3.3V
ENIN CEXT
V
IN
3.3V
1.2V
DC/DC
IN
OUTEN
ENABLE
CONTROL
12
t
EN1
t
EN2
t
EN3
EXTERNAL
DISABLE
12V
3.3V
2.5V
1.8V
1.2V
4591-028
Figure 23. Typical ADM1085 Application Circuit
